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Donald C. Cox

IEEE Personal Communications

pp. 20 ~ 35, April 1995

Wireless Personal Communications:What Is It?

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Introduction

• Hardly a week goes by without one seeing an articleon the wireless personal communications (WPC)appearing in a popular U.S. newspaper or magazine.

• What is WPC?– Paging ? or Messaging?

– Data System? or Access to NII?

– Cellular Radio? or Cordless Telephones?

– Satellites?

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Background and Issues

• The clearest ingredients in all of the WPC activity arethe desire for mobility in communications and to befree from tethers.

• Two different evolutions of WPC are data (packet-oriented) and voice (circuit-oriented) communications.

• Superimposed on the voice-data is an important issuein both fixed and mobile forms.

• ATM based networks are an attempt to integrate theneed of both the packet-data and circuit-orientedcommunications.

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Background and Issues (cont.)

• The WPC can be categorized according the followingtwo main characteristics.

• Communications portability and mobility:– Within house or building (cordless telephone, WLAN)

– Within campus, town, city (cellular radio, WLANs, widearea wireless data, radio paging, extended cordlesstelephone)

– Throughout a state or region (cellular radio, wide areawireless data, radio paging, satellite-based wireless)

– Throughout a large country or continent (cellular radio,paging, satellite-based wireless)

– Throughout the world?!!

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Background and Issues (cont.)

• Communications by different applications:– Two-way voice.

– Data.

– Messaging.

– Video?

• It is clear why WPC today is not one technology, notone system, and not one service, but encompassesmany technologies, systems and services optimized fordifferent applications.

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Evolution of Technologies, Systems, andServices

• Technologies and systems that are currently providingor are proposed to provide, can be grouped into aboutsix relatively distinct groups.– Cordless Telephones.– Cellular Mobile Radio Systems.– Wide Area Wireless Data Systems– High-Speed Wireless LANs– Paging/Messaging Systems– Satellite-Based Mobile Systems

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Cordless Telephones

• Cordless Telephones (CT) provide low mobility, low-power, two-way tetherless voice communications.

• They have evolved to digital radio technologies in theforms of CT-2, and Digital European Telephone(DECT), and Industrial Scientific Medical (ISM) bandtechnologies in the U.S.

• Assumptions & Compromises– Few users per MHz (for high circuit quality).

– Few users per base unit.

– Large number of base units per unit area.

– Short transmission range.

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Cordless Telephones (Cont.)

• Base unit are located in places where peoplecongregate, e.g., along city streets and in shoppingmalls, train stations, etc.

• Handsets registered with the phone-point provider canplace calls when within range of a telepoint.

• CT-2 does not provide capability for handoff.

• DECT can provide handoff active calls from one baseunit to another as user move, and can “page” or “ring”handsets as a user walks through areas covered bydifferent base units.

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Cordless Telephones (Cont.)

• Technology Similarities:– 32 kb/s adaptive differential pulse code modulation

(ADPCM) digital speech encoding: an internationalstandard.

– Average transmitter power <= 10 miliwatts

– Low-complexity radio signal processing.

– Low transmission delay, e.g., < 50 ms, and for CT-2 < 10 msround trip.

– Simple frequency-shift modulation and noncoherentdetection.

– Dynamic channel allocation

– Time division duplex (TDD)

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Cellular Mobile Radio Systems

• Cellular mobile radio systems are becoming known ashigh-tier Personal Communications Service (PCS)which provide high-mobility, wide-ranging, two-waytetherless voice communications.

• Transmitter power are 100 times compared to that ofCT (about 2 watts for cellular).

• Standard systems include Global Standard for Mobile(GSM) in Europe, Japanese or Personal DigitalCellular (JDC or PDC) in Japan, and U.S. TDMAdigital cellular known as USDC or IS-54.

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Cellular Mobile Radio Systems (Cont.)

• Assumptions and Compromises– Max users per MHz (for reducing communication cost).

– Max the users per cell site (for reducing communicationcost).

– High transmitter power consumption.

– High user-set complexity.

– Low circuit quality.

– High network complexity.

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Cellular Mobile Radio Systems (Cont.)

• Cellular radio has also been evolving for a few yearsin a different direction, toward very small coverageareas or microcells.

• This evolution provides increased capacity in areashaving high user density, and improved coverage ofshadowed areas.

• Microcells permit lower transmitter power and lessexpensive than conventional cell sites.

• Thus, the microcell increases system capacity andreduces the cost per available radio channel.

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Cellular Mobile Radio Systems (Cont.)

• Commonalties for the Cellular Mobile Systems:– Low bit-rate speech coding; <= 13 kb/s with some <= 8 kb/s.

– Some implementations make use of speech inactivity.

– High transmission delay; about 200 ms round trip.

– High complexity signal processing, both for speechencoding and for demodulation.

– Fixed channel allocation.

– Frequency division duplex (FDD).

– Mobile/portable set power control.

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Wide Area Wireless Data Systems

• Assumptions and Compromises:– High mobility

– Low data rate digital communication

• Deployed packet radio systems:– ARDIS in U.S: 4.8 kb/s

– RAM mobile data network based on Ericsson MobitexTechnology: 8 kb/s

– Cellular Digital Packet Data (CDPD): 19.2 kb/s

– Metricom use microcells technology: 75 kb/s

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High-Speed Wireless Local-Area Networks(WLANS)

• Assumptions:– Low mobility high speed data communication.

– Operates within confined region.

• Data rates ranging from hundreds of kb/s to more than10 MB/s.

• The best description of the WLAN is “having severebirth pains”. An IEEE standards committee, 802.11,has been attempting to put some order into this topic.

• There are two alternative organizations:– Centralized control via base station

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High-Speed Wireless Local-Area Networks(WLANS) Cont.

– Self-organization ad-hoc: every terminal has the samefunction as every other terminal, and networks are formedby communications exchanges among terminals.

• Three WLAN activities:– European Telecommunications Standards Institute (ETSI) to

produce a standard for High Performance Radio Local AreaNetwork (HIPERLAN) a 20 MB/s WLAN to operate near 5GHz.

– The UCB Infopad project based on DS spread spectrum.

– The UCLA project is aimed at peer-to-peer network anduses FH.

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Paging/Messaging Systems

• Paging can be categorized as one-way messaging overwide areas.

• High transmitter power (hundreds of watts tokilowatts), and high antennas at the fixed base stations.

• It has evolved from the one-bit message, “someonewants you,” to multi-bit messages from, the callingparty’s telephone number to short e-mail textmessages.

• Another evolutionary is two-way paging.

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Satellite-Based Mobile Systems

• Satellite-based systems are wide-area coverage,expensive, base station systems.

• The strength of satellite systems is their ability toprovide large regional or global coverage to usersoutside buildings.

• It is very difficult to cover inside buildings or evenlocations shadowed by buildings, tree or mountains.

• It is also difficult for frequency reuse results in lowcapacity along with the wide overall coverage.

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Satellite-Based Mobile Systems (Cont.)

• Proposed satellite systems range from– Low-earth-orbit (LEOS) having tens to hundreds of

satellites, through

– medium height systems (MEOS) to

– geostationary orbit systems (GEOS), having fewer than tensatellites.

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Evolution Toward the Future and to Low-Tier Personal Communications Services

• All of the technologies in the previous sectionsprovide WPC, and all do to some extent.

• The above systems aimed providing the followingfeatures.– High Quality Voice and Data.

– Economical Service.

– Privacy and Security of Communication.

• Taking characteristics from cordless, cellular, WLANssuggests the following attributes for the low-tier PCS:

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Evolution Toward the Future and to Low-Tier Personal Communications Services

– 32 kb/s ADPCM speech encoding

– Flexible radio link architecture that will support multipledata rates.

– Low transmitter power (<= 25 mW average) will result inmicrocells.

– Low complexity signal processing to minimize powerconsumption.

– Low co-channel interference and high coverage area designcriteria.

– Four-level phase modulation with coherent detection tomaximize radio link performance and capacity with lowcomplexity.

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Evolution Toward the Future and to Low-Tier Personal Communications Services

– FDD to relax the requirement for synchronizing base stationtransmission over a large region.

• On the voice side:– Cellular Radio, i.e., high-tier PCS, and

– Cordless telephone, i.e. low-tier PCS.

• On the data side:– Wide area data, i.e., high-tier data PCS, and

– WLANs perhaps a form of low-tier PCS.

• Low-tier PCS has a potential market of over 100million subscribers in the USA.

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Quality, Capacity, and Economics Issues

• High-tier PCS has a 30 times base station capacityover low-tier system.

• However, make such a base station capacitycomparison without including quality is notmeaningful.

• Cost Estimation– High-tier PCS: $5,555/circuit

– Low-tier PCS: $14/circuit (quality same as the high-tier)

– Low-tier PCS: $222/circuit (quality higher than high-tier)

• The cost of low-tier PCS is significantly better than forhigh-tier PCS.

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Other Issues

• Improved battery life for mobile devices.

• Suitability of high complexity spread spectrum/CDMAtechnologies for low cost, low power, low-tier PCS.

• Single handset and hands-free phones in vehicles.

• Integrated low-tier pocket phones with high-tiercellular mobile phones.– Intelligence between the internal ports and mobile sets could

interact with cellular mobile, air-ground, or satellitenetworks.

• High-tier to low-tier or low-tier to high-tier dual mode

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Conclusions

• Wireless personal communications have differentdegrees of mobility for operation in differentenvironments.

• Three large applications or services:– High-tier PCS (current cellular radio): make use of large

complex expensive cell sites.

– Low-tier PCS: increase capacity by reducing the spacingbetween base stations.

– High-speed wireless local-area networks (WLANS): manydifferent products being offered by many different vendors.

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Summary

• Digital Cordless Telephones– Strength: good circuit quality; long talk time; small

lightweight battery; low cost sets and service.

– Limitations: limited range; limited usage regions.

– Evolutionary trends: phone points in public places;wireless PBX in business.

– Remaining limitations and issues: limited usage regionsand coverage holes; limited or no handoff; limited range.

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Summary (Cont.)

• Digital Cellular Pocket Handsets– Strength: widespread service availability.

– Limitations: marginal circuit quality; limited talk time;large heavy batteries; high cost sets and service; holes incoverage and poor in-building; limited data capabilities;complex technologies.

– Evolutionary trends: microcells to increase capacity andin-building coverage, and to reduce battery drain satellitesystems to extend coverage.

– Remaining limitations and issues: limited talk time andlarge battery; marginal circuit quality; complextechnologies.

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Summary (Cont.)

• Wild Area Data– Strength: digital messages.

– Limitations: no voice; limited data rate; high cost.

– Evolutionary trends: microcells to increase capacity andreduce cost; share facilities with voice systems.

– Remaining limitations and issues: no voice; limitedcapacity.

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Summary (Cont.)

• Wireless Local Area Networks (WLANs)– Strength: high data rate.

– Limitations: insufficient capacity for voice; limitedcoverage; no standards, chaos.

– Evolutionary trends: hard to justify.

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Summary (Cont.)

• Paging/Messaging– Strength: widespread coverage; long battery life; small

lightweight sets and batteries; economical.

– Limitations: one-way message only; limited capacity.

– Evolutionary trends: two-way messaging and/or voice;capacity.

– Remaining limitations and issues: two-way link cannotexploit the advantage of one-way link asymmetry.